Lunate fractures most commonly occur secondary to a fall on an outstretched hand and have a notable risk of associated carpal instability. The lunate is situated in the proximal carpal row and has ligamentous attachments essential in carpal stability. The LT ligament maintains the lunotriquetral joint, with disruption resulting in volar intercalated segmental instability (VISI). The scapholunate ligament mirrors this attachment on the radial side, and injury to this ligament can cause dorsal intercalated segmental instability The vascular supply of the lunate is also important in fracture treatment because up to 20% of lunates have a volar-dominant blood supply, putting the lunate at risk for osteonecrosis with volar lip injuries. In addition, given the similar radiographic presentation, Kienbock disease must be ruled out when evaluating for lunate fractures. Kienbock disease typically presents with lunate collapse and sclerosis, as defined by the Lichtman classification.
A thorough evaluation of the hand is essential, given the high incidence of associated injuries in these cases. In addition, these fractures are difficult to note on standard radiographs and CT scans are often necessary to reveal the full fracture pattern. MRIs can be used to evaluate for ligamentous injuries.
Fractures of the lunate can be divided into volar lip, dorsal lip, and body fractures. The widely accepted mechanism of injury for most fractures of the lunate is an axial load through the capitate with the wrist in hyperextension and ulnar deviation resulting in a coronal body fracture (Figure 7, A). Nondisplaced fractures without evidence of carpal instability can be managed with short arm cast immobilization for 4 to 6 weeks. These injuries, especially those with volar or dorsal-radial comminution, must be monitored closely for displacement because of the high incidence of carpal instability. Large displaced fractures and any fractures with evidence of carpal instability require open reduction and internal fixation. Volar avulsions can impair perfusion and put the entire lunate at risk for osteonecrosis. Fixation is accomplished with compression screws and K-wire fixation for substantial osseous fragments (Figure 7, B). Suture anchor repair with K wire stabilization to adjacent carpal bones can be used when the osseous fragment is too small to fix and carpal instability is present. The lunate can be offloaded by distracting the third ray and placing a K wire through the scaphoid into the capitate, which may help in more complex fracture patterns.
Imaging of a lunate body fracture treated with open reduction and internal fixation. Preoperative radiograph demonstrates fracture displacement with intra-articular extension (A). A posterior-to-anterior compression screw has been placed for fixation (B). (Reproduced with permission from Hsu AR, Hsu PA: Unusual Case of Isolated Lunate Fracture Without Ligamentous Injury. Orthopedics 2011;34:e785-e789. With permission from SLACK Incorporated.)
Outcomes in lunate fractures are highly dependent on the amount of initial displacement. In a review of 34 lunate fractures, nondisplaced fractures were found to overwhelmingly progress to union without complication. In 14 cases of displaced lunate fracture with associated carpal dislocation, eight were complicated by osteonecrosis and nonunion or required a salvage procedure. Therefore, aggressive management is warranted in cases with fracture displacement and/or carpal instability to avoid these outcomes.
J Am Acad Orthop Surg. 2020;28(15):e651-e661. © 2020 American Academy of Orthopaedic Surgeons